This disclosure relates to syringes and, in particular, to a hypodermic syringe having a retractable needle guard for the purpose of preventing accidental needle sticks. Most syringes used today for medical or laboratory purposes are sold as disposable items intended to be used only once. Disposal of such syringes has posed a safety hazard for the individuals who use the syringes as well as for those who dispose of them. With the onset of AIDS, the concern for infection due to accidental needle sticks from used syringes has increased and a number of different devices have been proposed to minimize the possibility of spreading infectious disease due to accidents of this type.
One approach to this problem is to provide a retractable shield which, after the syringe has been used, can be pulled to an extended position where it covers the needle, making it difficult for an individual to accidentally contact the needle. A common feature of such constructions is that when the shield is pulled to its extended position, it is locked so that it cannot be retracted (thus exposing the needle) except by application of extraordinary force.
A number of such constructions have been proposed to satisfy the general requirement that the needle be permanently covered after the syringe has been used. Some of these constructions involve twist-to-lock mechanisms and, in others, locking occurs automatically when the shield is fully extended. These known devices satisfy many of the functional requirements of a needle shield and require, in most cases, modification of the standard syringe construction.
Those devices which lock in response to axial movement to the extended position, (i.e., without any rotation) have certain inherent drawbacks that result primarily from the requirement that substantial force be exerted axially to lock the shield in its extended position. In the first place, the likelihood of unintentional and irreversible locking is greater with such devices than with those devices which require rotation to lock. Also, it is difficult to verify that the shield is locked upon such forcible extension without attempting to retract the shield, which increases the possibility of unintended exposure of the needle. Further some of the safety syringes currently available allow the shield to be pulled axially from the syringe with only moderate applied force and or to be removed with moderate wiggling which has been attributed to the use of relatively soft polymers in combination with relatively small protrusions as the engaging elements of the shield and/or other components of the safety syringe. Finally, if the user's hand should slip from the shield while exerting the force necessary to extend the shield to the locked position, the user's hand may reflexively rebound back onto the needle point if the shield does not actually lock.
Accordingly, it is an object of this disclosure to provide a protective shield of the type described which provides a relatively inexpensive protective shield which satisfies the functional requirements of a needle shield and includes none of the drawbacks mentioned above.
Another object is to provide an extendable needle shield for a syringe which performs all of the necessary functions of such a shield and which is particularly well suited to an automated process of manufacture.
A further object of the disclosure is to provide an extendable needle shield for a safety syringe which is improved from the points of view of safety, functional utility, and cost of manufacture.